1. Pure states and approximate identities;Aarnes,1969
2. Power factorization in Banach algebras with a bounded approximate identity;Allan;Studia Math.,1976
3. Complete Normed Algebras;Bonsall,1973
4. Numerical Ranges of Operators on Normed Spaces and of Elements of Normed Algebras;Bonsall,1971
5. Factorization in group algebras;Cohen;Duke Math. J.,1959